1. Field of the Invention
The present invention relates to an electromagnetic actuator as an electro-mechanical converter using electromagnetic force, optical scanner and manufacturing method. More particularly, the present invention relates to a micro-electromagnetic actuator, which can be manufactured by a micro-machining technology, being easier to control and able to have larger strokes than a conventional electromagnetic actuator, and its manufacturing method.
2. Related Background Art
The mainstream of actuators manufactured by conventional micro-machining technologies has been actuators using an electrostatic force or piezoelectric phenomenon. However, actuators using electromagnetic power are also increasingly being developed as it is becoming easier to use magnetic materials by a micro-machining technology in recent years.
FIG. 7 is an example of an electromagnetic linear actuator for positioning a hard disk head (U.S. Pat. No. 5,724,015). The actuator in FIG. 7 comprises fixed cores 1004a and 1004b, coils 1005a and 1005b wound around the fixed cores fixed on a substrate (not shown in the figure) and a movable element 1003 supported by means of a spring 1007 in such a way that the movable element 1003 is movable relative to the fixed cores 1004a and 1004b. These structures are manufactured on the substrate using a micro-machining technology.
When the coil 1005a of this actuator is energized, the movable element 1003 is attracted to the fixed core 1004a and the movable element 1003 moves leftward in the figure. On the contrary, when the coil 1005b is energized, the movable element 1003 moves rightward in the figure. The force F1 generated by this actuator is given by the following expression:                               F          1                =                  0.5          ⁢                      μ            0                    ⁢                      N            1            2                    ⁢                      i            1            2                    ⁢                      w            1                    ⁢                      t            1                    ⁢                      x            1                          -              2                                                          (        1        )            where μ0 is vacuum magnetic permeability; N1, the number of coil turns; i1, a current that flows through the coils 1005a and 1005b; w1, width of the magnetic pole; t1, thickness of the magnetic pole; and x1, length of the gap. The displacement of this actuator is calculated from the following relationship, where the spring constant of the spring 1007 is assumed to be k1:F1=k1x1  (2)
However, as is clear from expression (1), with the actuator above, the generated force F1 is not determined by the current i1 alone and is inversely proportional to the square of the gap x1. Thus, the actuator above has a problem that it is hard to control.
Another problem is that when the initial gap is increased, the generated force reduces suddenly, making it impossible to increase strokes.